Logarithmic light intensifier for use with photoreceptor-based implanted retinal prosthetics and those prosthetics

ABSTRACT

This invention is for directly modulating a beam of photons onto the retinas of patients who have extreme vision impairment or blindness. Its purpose is to supply enough imaging energy to retinal prosthetics implanted in the eye which operate essentially by having light (external to the eye) activating photoreceptors, or photo-electrical material. The invention provides sufficient light amplification and does it logarithmically. While it has sufficient output light power, the output light level still remains at a safe level. Most preferred embodiments of this invention provide balanced biphasic stimulation with no net charge injection into the eye. Both optical and electronic magnification for the image, as for example, using an optical zoom lens, is incorporated. Otherwise, it would not be feasible to zoom in on items of particular interest or necessity. Without proper adjustment, improper threshold amplitudes would obtain, as well as uncomfortable maximum thresholds. Therefore, to adjust for these, a way of proper adjustment for the threshold amplitudes and maximum comfortable thresholds is provided. Furthermore, to the extent that individual stimulation sites in the retina give different color perceptions, upon stimulation, then colors of the viewed scene is correlated with specific stimulation sites to provide a certain amount of color vision.

[0001] This application claims the benefit of U.S. ProvisionalApplication No. 60/125,875, filed Mar. 24, 1999.

FIELD OF THE INVENTION

[0002] This invention, relates generally to retinal prosthetics and moreparticularly to a method and apparatus for enhancing retinal prostheticperformance.

[0003] This invention relates to directly modulating a beam of photonsof sufficient energy onto retinal prosthetic implants of patients whohave extreme vision impairment or blindness.

BACKGROUND OF THE INVENTION

[0004] A healthy eye is has photosensitive retinal cells (e.g. rods andcones) which react to specific wavelengths of light to trigger nerveimpulses. Complex interconnections among the retinal nerves assemblethese impulses which are carried through the optic nerve to the visualcenters of the brain, where they are interpreted. Certain forms ofvisual impairment are primarily attributable to a malfunction of thephotosensitive retinal cells. In such cases, sight may be enhanced by aretinal prosthesis implanted in a patient's eye. Michelson (U.S. Pat.No. 4,628,933) and Chow (U.S. Pat. Nos. 5,016,633; 5,397,350; 5,556,423)teach a retinal implant, or implants, of essentially photoreceptorsfacing out of the eye toward the pupil, each with an electrode which canstimulate a bipolar, or similar, cell with an electrical impulse. Thisbipolar cell is acted upon by the electrical stimulus, to sendappropriate nerve impulses essentially through the optic nerve, to thebrain.

[0005] This invention is postulated as a necessary complement to thistype of prosthesis, because the photoreceptors do not appear to besensitive enough to the ordinary levels of light entering the eye inthat not enough current is produced to sufficiently stimulate theretinal cells. Consequently, a light amplifier, or “helper” device wouldbe needed. That device is the invention herein described, which alsoincludes special characteristic implants.

[0006] Furness, et al. teach a “virtual retinal display”, U.S. Pat. No.5,659,327, where “The virtual retinal display . . . utilizes photongeneration and manipulation to create a panoramic, high resolution,color virtual image that is projected directly onto the retina of theeye . . . there being no real or aerial image that is viewed via amirror or optics.” Richard, et al. teach, U.S. Pat. No. 5,369,415, “ . .. a direct retinal scan display including the steps of providing adirected beam of light, modulating the beam of light to impress videoinformation onto the beam of light, deflecting the beam in twoorthogonal directions, providing a planar imager including an input forreceiving a beam of light into the eye of an operator which involves aredirection diffractive optical element for creating a virtual imagefrom the beam of light on the retina of the eye, and directing the beamof light scanned in two orthogonal directions and modulated into theinput of the planar imager and the output of the planar imager into theeye of an operator.”

[0007] Sighted individuals can use these devices above for theirintended uses. However, they appear unsuitable for use by blindindividuals with implanted retinal prosthetics of thephotoreceptor-electrode kind. It would seem that they do not provideenough light power. Moreover, light amplitude cannot be arbitrarilyincreased because according to Slinly and Wolbarscht, Safety with Lasersand Other Optical Sources, the retinal threshold damage is 0.4 Joulesper square centimeter.

SUMMARY OF THE INVENTION

[0008] The present invention is directed to a method and apparatus forproviding enhanced retinal prosthetic performance. More particularly,the invention is directed to a light amplifier and electrical circuitryfor driving an implanted retinal prosthesis to maximize electricalstimulation of the retinal nerves or cells, while avoiding damagethereto. The invention is also directed to improved implanted retinalprostheses, which maximize the advantages of the light amplifier.

[0009] In accordance with one aspect of the invention, light reflectedfrom a viewed image (i.e., input image) is passed through a lightamplifier to produce an output image which is applied to thephotoreceptor array of a retinal prosthesis. The gain (or “transferfunction”) of the light amplifier enables the photoreceptor array todrive output electrodes for producing retinal nerve impulses ofsufficient magnitude to enhance perceived sight.

[0010] In accordance with another aspect of the invention, the lightamplifier preferably compresses the range of light intensity, e.g.,logarithmically, to enable maximum light amplification withoutoverdriving the prosthetic photoreceptors.

[0011] In accordance with another aspect of the invention, theelectrical stimulation of the retinal nerves is preferably pulsed, i.e.,periodically interrupted to avoid any damage attributable to peakmagnitude electrical signals. Periodic interruption can be implementedmechanically by a shutter periodically interrupting the light incidenton the photoreceptor array and/or electrically via an appropriate waveshaping circuit.

[0012] In accordance with another aspect of the invention, the implantedprosthetic's electrodes generate a sequence of positive and negativepulses to avoid producing a net charge in the eye. Successive pulses arepreferably spaced in time by an interval Δt.

[0013] Four preferred embodiments are described. In accordance with thefirst embodiment of the invention a single wavelength is relied upon toactivate a combined photodetector-electronics-electrode implanted unitwhich then produces a negative pulse, followed by a time delay, followedby a positive pulse. A photoreceptor implanted in the eye acts toproduce an electrical stimulation with an equal amount of positive andnegative charge. A single light wavelength is received by thephotoreceptor. That single wavelength contains extractable energy. Italso contains information, which may be encoded by amplitude modulation,frequency modulation, phase shift methods or pulse width modulation, forexample. The photoreceptor activates an electrode with associatedelectronics. The electronics produces a negative pulse followed by atime delay followed by a positive pulse. A net charge of zero isintroduced into the eye by the electrode-originating electrical pulses.The preferred delay time is in the range 0.1 millisecond to 10milliseconds, with the delay time of 2 milliseconds is most preferred.When the retinal cell is not being electrically stimulated, it returnsto a rest and recovery state. It is then in a state, electrically, thatit was in prior to stimulation by the first electrical stimulation.

[0014] In accordance with the second embodiment, a first wavelength isused to stimulate a first set of “electronic” photoreceptors. Thesephotoreceptors are connected so that the stimulation of the attached, orassociated, electrodes results in a negative pulse. This negative pulseprovides retinal cell stimulation. Then the shutter cuts in and stopslight transmission to the eye. The retinal cell is in a rest andrecovery state so that it returns, electrically, to the state it was inprior to stimulation by the first particular wavelength of light. Asecond particular wavelength of light then stimulates a second set ofphotoreceptors which are sensitive to that wavelength of light; whilethe first set of photoreceptors are not affected. This second set ofphotoreceptors is connected so that the stimulation of the attached, orassociated, electrodes results in a positive pulse. The net chargeintroduced into the retinal cells must balance. So the positive chargeintroduced by the positive pulse must equal the negative chargeintroduced by the negative pulse. Again, the shutter cuts in and stopslight transmission. Again, the retinal cells rest and recover and theprocess repeats. An aspect of the second embodiment is using anelectro-optic, electronic or mechanical shutter to provide a period ofno electrical stimulation to the retinal cells targeted for electricalstimulation.

[0015] In accordance with a third embodiment, which is a cross, so tospeak, between the first and second embodiments two differentwavelengths and two different types of diodes, each responsive to acorresponding wavelength are used. In this embodiment, one wavelength isused to pump in a high constant level of light to supply power to theelectronics component. The other wavelength is used to send ininformation via amplitude, frequency, phase, pulse-width modulation, orcombinations thereof. The stimulation pulse from the electronics to theelectrode to the retinal cell is generated in a fashion similar to thepulses generated in the first embodiment, with a single wavelength.

[0016] A fourth embodiment is that of the logarithmic light amplifieritself, without any special implantable photoreceptors. This lastembodiment may require a low duty cycle when used with photoreceptorsconnected to a diode without any electronics. It may be able to relysufficiently upon the intrinsic capacitance of an oxidizable electrode,which acquires capacitance with the buildup of an insulating oxidizedlayer toward the ionizable fluid present in the eye as vitreous fluid,or fluid directly associated with the eye.

[0017] An image receiver with a first converter for the image, convertsthe image into electrical signals. The signals are amplified, basicallylogarithmically, so as to provide brightness compression for thepatient.

[0018] An aspect of the embodiments of the invention is that anamplified electrical signal is converted by a second converter into aphoton-based display; the photons of this display enter an eye throughthe pupil of the eye. Moreover, while the embodiments of the logarithmicamplifier invention have sufficient output light power, advantageously,the output light level still remains at a safe level. This aspect of theinvention corresponds to aspects of the action of the iris, as well asthe biochemistry of retinal cells, in the human eye in making possiblesight over many orders of magnitude of ambient brightness.

[0019] An aspect of the embodiments of the invention is incorporation ofboth optical and electronic magnification of the image, as for example,the incorporation of an optical zoom lens, as well as electronicmagnification. Consequently, it is feasible to focus in on items ofparticular interest or necessity.

[0020] With proper adjustment, proper threshold amplitudes of apparentbrightness would obtain, as well as comfortable maximum thresholds ofapparent brightness. Therefore, to adjust for these, an adjustmentaspect is incorporated in each embodiment, such that proper adjustmentfor the threshold amplitudes and maximum comfortable thresholds aremade.

[0021] Another aspect of the invention, which may be incorporated in allembodiments, is oriented toward making color vision available, at leastto a degree. To the extent that individual stimulation sites (e.g.,retinal cells generally, bipolar cells specifically) give differentcolor perceptions upon stimulation, the color of selected pixels of theviewed scene is correlated with a specificphotoreceptor-electronics-electrode units located so as to electricallystimulate a specific type of bipolar cell to provide the perception ofcolor vision.

[0022] In order to help implement both comfortable adjustment ofthreshold and maximum brightness, and color vision, the logarithmiclight amplifier also incorporates within itself, a data processing unitwhich, semi-autonomously, cycles through the variousphotodetector-electrode and combinations thereof, interrogates thepatient as to what the patient sees, the patient then supplies theanswers, setting up proper apparent brightness, proper apparent colorand proper perception. This setup mode is done by the use of a keyboard,display, and auxiliary processor, which are plugged into the dataprocessing unit of the logarithmic light amplifier during the setupprocedure.

[0023] A scanning laser feedback is provided in different embodiments ofthe invention to keep the scanner laser scanning the correct locations.An imaging of the reflected scanning laser reflected back from theretinal implant is used to provide real-time feedback information,utilizing a second imager viewing into the eye and a data processor unittied into the scanning laser scan control unit.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The above and other features and advantages of the invention willbe more apparent from the following detailed description wherein:

[0025]FIG. 1 shows the logarithmic light amplifier with shutter, showingthe incoming scene or view photons on the right and the eye on the left;

[0026]FIG. 2a shows a laser being modulated by a video signal andscanning the full extent of the implanted retinal prosthesis;

[0027]FIG. 2b shows a photoreceptor, associated electronics, and anassociated electrode;

[0028]FIG. 2c shows the apparatus of FIG. 2b but in a more rounded,smoother packaged form, likely more amenable for implantation into theeye;

[0029]FIG. 3 depicts tuned photodetectors on an implanted retinalprosthesis;

[0030]FIG. 4 shows a sample waveform possible with the apparatus shownin FIG. 3;

[0031]FIG. 5 shows two different wavelengths, one to send in power, theother to send in information, to a single unit with two differentlysensitive photoreceptors, one electronics package and one electrode;

[0032]FIG. 6 summarizes three embodiments as shown previously;

[0033]FIG. 7 shows the external logarithmic amplifier (as “glasses”), aportable computer with mouse and joystick as setup aids;

[0034]FIG. 8 shows an implant unit (old in the art) with a photoreceptorand an electrode;

[0035]FIG. 9a shows a light-electronic feedback loop for knowinglocation on implant being scanned;

[0036]FIG. 9b shows one of different possible fiduciary markingsincluding here points and lines for aiding knowing location on implantbeing scanned.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0037] The following description is of the best mode presentlycontemplated for carrying out the invention. This description is not tobe taken in a limiting sense, but is merely made for the purpose ofdescribing the general principles of the invention. The scope of theinvention should be determined with reference to the claims.

[0038] This invention provides amplified light for artificialphotoreceptors implanted in the eye of a patient who has lost the use ofhis/her normal photoreceptor retinal cells. The purpose of thisamplified light is to effectively stimulate the artificialphotoreceptors. The artificial photoreceptors, in turn, provideelectrical stimulation through associated electrodes, usually via someelectronics, to retinal cells, which are normally stimulated by livingretinal photoreceptors such as cones and rods. The retinal cells, whichget electrically stimulated by way of the artificial photoreceptors, aretypically bipolar cells. This stimulation to these non-photoreceptorretinal cells allows the patient to have at least some perception ofwhat a normal eye would see. In order not to damage the retinal cells,light is fed to the photoreceptor-electrode stimulators in the followingways.

[0039] Four preferred embodiments are described. In the first embodimenta single wavelength is relied upon to activate a combinedphotodetector-electronics-electrode implanted unit which then produces anegative pulse, followed by a time delay, followed by a negative pulse.In the first embodiment, a photoreceptor implanted in the eye acts toproduce an electrical stimulation with an equal amount of positive andnegative charge. A single light wavelength is received by thephotoreceptor. The photoreceptor activates an electrode with associatedelectronics. The electronics produces a negative pulse followed by atime delay followed by a positive pulse. A net charge of zero isintroduced into the eye by the electrode-originating electrical pulses.The preferred delay time is in the range 0.1 millisecond to 10milliseconds, with the delay time of 2 milliseconds is most preferred.When he retinal cell is not being electrically stimulated, it returns toa rest and recovery state. It is then in a state, electrically, it wasin prior to stimulation by the first electrical stimulation.

[0040] Starting with the logarithmic amplifier, an image receiver with afirst converter for the image, converts the image into electricalsignals. The signals are amplified, basically logarithmically, so as toprovide brightness compression for the patient. The amplified electricalsignal is converted by a second converter into a photon-based display;wherein said photons of said display enter an eye through a pupil ofsaid eye.

[0041] Photons (102) from a viewed scene (not shown) enter thelogarithmic amplifier (1000) by way of the lens (101). The lightamplifier (1000) has an image receiver (1), a first converter (103) ofthe image into electrical signals, an amplifier (2) of said electricalsignals whereby the overall amplification of said electrical signalaccording to a definite functional relationship between input signal tothe amplifier and an output signal from the amplifier, a secondconverter (107) of said amplified electrical signal into a photon-baseddisplay (7); such that the of display photons (108) enter an eye (5)through the pupil (105) of the eye (5). In the case where the imager (1)is a type of video camera, the image receiver and conversion toelectrical signals may occur in a package (old in the art).

[0042] A display (7) that is a source of photons such as a laser(coherent light source) (7), or a non-coherent source such as coloredLEDs (7), or a plasma display (7), is used to send photons directly toan implant near the retina. These displays (7) are made very bright, butnot such as to impact negatively on the eye. In our cases, the patienthas sufficient retinal degeneration so as to be unable to see withoutthe aid of a retinal prosthetic. In the case where the display (photonsource) is a laser (7), that laser is 15 scanned over the implantedphotodetector-electronics-electrode array (FIG. 2, (8) in accordancewith the scene being displayed to the eye. A scanning laser is a laserwith scanning means (old in the art).

[0043] Referencing FIG. 2a, the video signal (6) is applied to ascanning laser (7), a scanning laser being a laser with scanning means(old in the art). The scanning laser (7) is scanned over the retinalprosthesis in a square or rectangular pattern or in a raster patternwith an exact fit to the prosthesis (8). The video signal (6) suppliesamplitude from the data processor (FIG. 1, (2)), and if desired (seeFIG. 1), color information, of the scene being viewed, from theindividual color amplifiers (3) to the laser (7), which information isused to modulate the laser.

[0044] In a preferred mode, the light amplifier (1000) is a logarithmicamplifier. In another preferred mode, the amplifier amplifies accordingto a different function than the logarithmic function or a modifiedlogarithmic function, for example, an algebraic function such as apolynomial function multiplied by the logarithmic function.

[0045] The imager or camera lens is shown schematically as (101). Thesignal is logarithmically amplified as a whole at the electronicprocessor (2), or the individual RGB (red, green, blue) or RGBY (red,green, blue, yellow) color components are individually logarithmicallyamplified (3). Another color component mix of white light may be used.The individual amplification (3) of separate color components allows forthe relative super-amplification of one color to which thephotoreceptors are particularly sensitive. If only a “black-and-white”contrast image is displayed, the “white” part of that image islogarithmically translated to the color, i.e., wavelength, to which thephotoreceptors are most sensitive. This feature includes shifting thewavelength toward or to the near infrared or toward or to the nearultraviolet, according to what is needed to optimize the response of theimplanted photosensitive elements. Consequently, a mapping of theincoming image data to an appropriate output is possible. This mappingcould be complex, for example, producing biphasic waveforms as shown inFIG. 4 by appropriate timing of two lasers operating at differentwavelengths and photosensitive elements uniquely sensitive to thesewavelengths.

[0046] In a preferred mode, individual RGB (red, green, blue) or RGBY(red, green, blue, yellow) color components are amplified separately(3), or amplified together (2) and separated out (3) after theamplification. These color components may be used to stimulateparticular photosensitive elements of the retinal implant(s). Forexample, a cell (“blue-sensation”) producing a sensation of blue coloris stimulated when the scene being transmitted to the eye has blue,which in the projected (into the eye) scene would have blue in thevicinity of that blue-sensation cell.

[0047] The logarithmic amplification is necessary to compress the rangeof original brightness. The normal eye does this automatically ofclosing down the pupil size, squinting and employing otherelectrochemical cellular mechanisms. This light amplifier accomplishesthis necessary task by electronic logarithmic light amplification. Thelight amplifier also includes an adjustable transformer or magnificationof image size. A shutter or electronically turning the scanning laser onand off are not a necessary part of this embodiment.

[0048] In the second preferred embodiment of the light amplifier two ormore wavelengths are used to communicate light energy to the eye toallow balanced biphasic stimulation with no net charge injection intothe eye. A first wavelength is used to stimulate a first set ofphotoreceptors. These photoreceptors are connected so that thestimulation of the attached, or associated, electrodes results in anegative pulse. This negative pulse provides retinal cell stimulation.Then the shutter cuts in and stops light transmission to the eye. Thetime of this light interruption is preferred in the range 0.1millisecond to 10 milliseconds, with the time of 2 milliseconds mostpreferred. The retinal cell is in a rest and recovery state so that itreturns, electrically, to the state it was in prior to stimulation bythe first particular wavelength of light. A second wavelength of lightthen stimulates a second set of photoreceptors which are sensitive tothat wavelength of light; while the first set of photoreceptors are notaffected. This second set of photoreceptors is connected so that thestimulation of the attached, or associated, electrodes results in apositive pulse. The net charge introduced into the retinal cells mustbalance, or equal, the net charge introduced by the negative pulse.Again, the shutter cuts in and stops light transmission. Again, theretinal cells rest and recover and the process repeats.

[0049] In the second preferred embodiment, FIG. 3A, two scanning lasers,(9) and (10), are supplied with video signals, with each laser operatingat a different wavelength. Advantageously, two or more photoreceptors(13), (14) are on the implant. The two types of photoreceptors (13),(14), are tuned to different frequencies of light, each of thefrequencies being that of one of the emitting frequencies of theexternal lasers (9), (10). FIG. 3B shows two incoming frequencies oflight, (301) and (302). The light sources for the dual light frequencies(301), (302) is a unit (304) which is downstream in the information flowfrom the imager (FIG. 1, (101), (1), (103)) and amplifiers (FIG. 1, (2),(3)). The final output from the amplification stages is connectedelectrically or electromagnetically to the dual light frequency sources(304), in particular, dual scanning lasers operating with differentwavelengths of light output. Pairs (303) of different frequency (i.e.,wavelength) photoreceptors are placed on the eye-implant, each pairassociated with an electrode (not shown).

[0050] Together, the two types of photoreceptors (e.g., photodiodes)give rise to a biphasic current (FIG. 4) at each electrode (not shown).Initially the rest state appears (40). Next, one of the photoreceptors(13) has been activated by its corresponding laser (9). The currentamplitude is negative. (41). After a time (42), laser (9) andphotoreceptor (13) shut down and the amplitude returns to zero. Next,the other laser (10) actives its corresponding (in light wavelength)photoreceptor (14) and the amplitude is positive by an amount (43) andfor a duration (44). Nominally, in absolute value, (41)=(43), and(42)=(44). However, in the case this is not exact, then the parameters(44) and (43) can be altered such that (41)*(42)=(43)*(44), where *indicates multiplication. This can be accomplished by measuring (41) and(42) and then altering (43) or (44) or both to maintain charge balance.

[0051] A shutter (4) is part of the second embodiment. The shutter (FIG.1, (4)) is of a mechanical design (old in the art), or an electronicshutter (4) (old in the art) or an electro-optical shutter (4) (old inthe art). The shutter (4) cuts off light from the logarithmic lightamplifier (1000) to the pupil (105) of the eye (5). This decreases thetotal time that light strikes the photoreceptors (FIG. 3a, (13), (14)),(FIG. 3b, 303) Consequently, the time during which the bipolar, orsimilar cells, are stimulated is decreased. Because the eye is notfunctioning as originally intended, the bipolar, or similar, cells arethought to need this “down-time” to continue to function properly.

[0052] An aspect of this invention is the use of two or more wavelengthsto allow balanced biphasic stimulation with no net charge injection intothe eye. As long as a biphasic type of electrical stimulation, whereequal amounts of positive charge and negative charge in the form ofionic carriers or electrons or other charge carriers, enter the vitreousfluid of the eye, the electrical effect on the eye is not harmful. Ifdirect current is supplied to the eye, internally, a charge imbalanceresults. This excess of charge has been found to be harmful to cells.Consequently, direct current can harm the bipolar and other cells.Advantageously, the biphasic electrical stimulation tends to avoid thisharm to the cells because no excess charge accumulates.

[0053] A third embodiment that is a cross, so to speak, between thefirst and second embodiments uses two different wavelengths and twodifferent types of diodes, each responsive to a correspondingwavelength. In this embodiment, one wavelength is used to pump in a highconstant level of light to supply power to the electronics component.The other wavelength is used to send in information via amplitude,frequency, phase, pulse-width modulation, or combinations thereof. Thestimulation pulse from the electronics to the electrode to the retinalcell is generated in a fashion similar to the pulses generated in thefirst embodiment, with a single wavelength.

[0054] The third embodiment uses two different wavelengths and twodifferent types of diodes, each responsive to a correspondingwavelength. (See FIG. 3b, (301), (302)). In this embodiment, onewavelength (FIG. 5, (501)) is used to pump in a high constant level oflight to supply power to the electronics component (502). The otherwavelength (503) is used to send in information via amplitude,frequency, phase, pulse-width modulation, or combinations thereof to theelectronics component (502). The stimulation pulse from the electronics(502) to the electrode (504) to the retinal cell is generated in afashion similar to the pulses generated in the first embodiment, with asingle wavelength.

[0055] See FIG. 6. FIG. 6 summarizes in block form the preceding threeembodiments. In the first embodiment there is one wavelength (601) inputto a single diode (602) with electronics (603) and electrode (604).Either digitally or by analogue means, old in the art, a d. c. signaloccurring after the absorption of photons by the photoreceptor isconverted by the electronics to a signal (600) of the type shown in FIG.4, at the electrode. In the second embodiment, for two differentwavelengths (610), (611), both carrying power and information, impingingon two different photoreceptors (612), (613), the electronics (6033),digital or analogue, again produce the waveform (600) of FIG. 4 at theelectrode (604). In the third embodiment, for two differentphotoreceptors (620), (621), the first receiving a steady state powerwavelength (622), the second receiving a signal wavelength (623), theelectronics (6034), digital or analogue, produces the signal (600) ofFIG. 4 at the electrode (604). The electronic circuitry of (603), (6033)and (6034) may be different.

[0056] A fourth embodiment is that of the logarithmic light amplifier(1000) itself, without any special implantable photoreceptors. This lastembodiment may require a low duty cycle when used with photoreceptors(FIG. 8, (81)) connected to an electrode (82) without any electronics.It relies upon the intrinsic capacitance of an oxidizable electrode,which acquires capacitance with the buildup of an insulating oxidizedlayer toward the ionizable fluid present in the eye as vitreous fluid,or fluid directly associated with the eye.

[0057] In a first set of embodiments, the addition of a shutter (FIG. 1,(4)) with an off time of from 0.5 ms to 10 ms, most preferably 2 msprovides a mechanism to provide that off time (FIG. 4, (47), (48)).However, in a second set of embodiments, the time each laser is on canbe controlled by electronic means (old in the art) within the laser toprovide equal positive pulses and negative pulses, i.e., equal withrespect to total signed charge introduced into a retinal cell. The firstand second sets of embodiments may be completely or partiallycoincident.

[0058] Another aspect of all of the embodiments is incorporation of bothoptical and electronic magnification of the image, as for example, theincorporation of an optical zoom lens, as well:as electronicmagnification. Optical magnification of the image (see FIG. 1) isaccomplished by use of a zoom lens for the camera lens (101). Electronicmagnification is accomplished electronically in an electronic dataprocessing unit (2) or (3). Consequently, it is feasible to focus in onitems of particular interest or necessity.

[0059] With proper adjustment, proper threshold amplitudes of apparentbrightness obtain, as well as comfortable maximum thresholds of apparentbrightness. Therefore, to adjust for these, a sixth aspect isincorporated in all of the embodiments such that proper adjustment forthe threshold amplitudes and maximum comfortable thresholds can be made.

[0060] To makes color vision available, to a degree; another aspect isincorporated. To the extent that individual stimulation sites (e.g.,bipolar cells) give different color perceptions upon stimulation, thecolor of selected pixels of the viewed scene is correlated with aspecific pair of photoreceptors located so as to electrically stimulatea specific type of bipolar cell to provide the perception of colorvision

[0061] In order to help implement these last two aspects of thepreferred embodiments of this invention, apparent brightness control andthe presentment of apparent color, the logarithmic amplifier alsoincorporates within itself, a data processing unit which cycleselectrical pulses of varying amplitude and/or frequency and/or phaseand/or pulse width through the various photodetector-electrodes andspatial combinations thereof, and, interrogates the patient, who thensupplies the answers, setting up proper apparent brightness and apparentcolor. A different aspect of the embodiments utilizes a plug inaccessory data processor (FIG. 7, (71)) with display (72) and data inputdevice or devices such as a keyboard (73), mouse (74), or joystick (75).FIG. 7 show the plug in unit (71) which plugs (76) into the logarithmiclight amplifier (1000) to provide additional data processing ability aswell as expanded data input and data display capability.

[0062] In order for the scanning laser to correctly scan the retinalimplant prosthetic photoreceptors, it is helpful if some feedback isprovided to it. One aspect of the different embodiments is the presenceof a feedback loop using some of the reflected light from the scanninglaser itself. One aspect of the feedback loop is to use regions ofdifferent reflectivity on the surface of the retinal implant which allowthe location, or relative location, of the scanning laser light beam tobe determined.

[0063] A scanning laser feedback is provided in the differentembodiments of the invention. An imaging (FIG. 9a) of the retinalimplant from the reflected (92) incoming scanning laser beam (91), seeFIG. 9a, (7), (FIG. 1 and FIG. 2a, (7)), (FIG. 3a, (9,), (10)) reflectedback from the retinal implant (FIG. 9, (8)) can be used to providereal-time feedback information, utilizing a second imager (93) viewinginto the eye (5) and a data processor unit (94) tied into the scanninglaser's scan control unit (95).

[0064] Another aspect of the embodiments (FIG. 9b) utilizes multiplefiduciary reflective or light absorptive points (96) and/or lines (97)on the retinal implant (8) such that the frequency and signal pattern,more generally, (98), (99), (100) of the high reflectivity from thesereflective, or absorptive lines/point for a given rate of scanning bythe scanning laser (7) can be used to correct the scanning directionfrom the different frequency patterns, some indicating correct scanning,others indicating an incorrect scanning.

[0065] While the invention herein disclosed has been described by meansof specific embodiments and applications thereof, numerous modificationsand variations could be made thereto by those skilled in the art withoutdeparting from the scope of the invention set forth in the claims.

What is claimed is:
 1. Apparatus for enhancing the performance of aretinal prosthesis implanted in a patient's eye, said prosthesis beingcomprised of an array of photodetectors and a plurality of electrodesfor stimulating retinal nerves, said apparatus comprising: a lightamplifier mounted external to the eye and responsive to an input imagefor producing an output image related to said input image by a transferfunction G; said light amplifier being positioned so that said outputimage is incident on said implanted photodetector array; said pluralityof electrodes being responsive to said output image incident on saidphotodetector array for producing a sequence of negative and positiveelectrical pulses for application to said retinal nerves; and whereinsuccessive pulses are spaced in time by an interval Δt.
 2. A lightamplifier with photoreceptor-based implanted retinal prostheticscomprising: a. an image receiver; b. a first converter of said imageinto electrical signals; c. an amplifier of said electrical signals; d.an overall amplification of said electrical signal according to adefinite functional relationship between input signal to the amplifierand an output signal from the amplifier; e. a transformer of the imagesize; f. a second converter of said amplified electrical signal into aphoton-based display; wherein said photons of said display enter an eyethrough a pupil of said eye; g. wherein a photoreceptor implanted in theeye acts to produce an electrical stimulation with an equal amount ofpositive and negative charge; h. wherein a single light wavelength isreceived by the photoreceptor; i. wherein said photoreceptor activatesan electrode with associated electronics; j. wherein said electronicsproduces a negative pulse followed by a time delay followed by apositive pulse; k. whereby a net charge of zero is introduced into theeye by the electrode-originating electrical pulses.
 3. The lightamplifier of claim 2 wherein the image receiver and the first converterof said image into electrical signals is a video camera.
 4. The lightamplifier of claim 2 wherein said amplifier logarithmically amplifiessaid electrical signal.
 5. The light amplifier of claim 2 wherein thetransformer of the image size is a magnifier of the image size.
 6. Thelight amplifier of claim 5 wherein the magnifier of the image size is anelectronic magnifier.
 7. The light amplifier of claim 5 wherein themagnifier of the image size is an optical zoom lens.
 8. A lightamplifier with photoreceptor-based implanted retinal prostheticscomprising: a. an image receiver; b. a first-converter of said imageinto electrical signals; c. an amplifier of said electrical signals; d.an overall amplification of said electrical signal according to adefinite functional relationship between input signal to the amplifierand an output signal from the amplifier; e. a transformer of the imagesize; f. a second converter of said amplified electrical signal into aphoton-based display; wherein said photons of said display enter an eyethrough a pupil of said eye; g. a periodic interrupter of the photonstream from said photon-based display; h. wherein a plurality ofexternal-to-the-eye wavelengths provides light stimulation to an equalnumber of types, as the number of the plurality of wavelengths, ofappropriately tuned photoreceptors, implanted in the eye, which act toresult in electrical stimulation from associated electrodes with anequal amount of positive and negative net charge, as measured by amountof charge introduced into the eye. whereby the net charge introduced iszero.
 9. The light amplifier of claim 8 wherein the image receiver andthe first converter of said image into electrical signals is a videocamera.
 10. The light amplifier of claim 8 wherein said amplifierlogarithmically amplifies said electrical signal.
 11. The lightamplifier of claim 8 wherein the transformer of the image size is amagnifier of the image size.
 12. The light amplifier of claim 11 whereinthe magnifier of the image size is an electronic magnifier.
 13. Thelight amplifier of claim 11 wherein the magnifier of the image size isan optical zoom lens.
 14. The light amplifier of claim 8 wherein theinterrupter of the photon stream is a mechanical shutter.
 15. The lightamplifier of claim 8 wherein the interrupter of the photon stream is anelectronic shutter.
 16. The light amplifier of claim 8 wherein theinterrupter of the photon stream is an electro-optical shutter.
 17. Alight amplifier with photoreceptor-based implanted retinal prostheticscomprising: a. an image receiver; b. a first converter of said imageinto electrical signals; c. an amplifier of said electrical signals; d.an overall amplification of said electrical signal according to adefinite functional relationship between input signal to the amplifierand an output signal from the amplifier; e. a transformer of the imagesize; f. a second converter of said amplified electrical signal into aphoton-based display; wherein said photons of said display enter an eyethrough a pupil of said eye; g. a periodic interrupter of the photonstream from said photon-based display; h. wherein a plurality ofexternal-to-the-eye wavelengths provides light stimulation to an equalnumber of types, as the number of the plurality of wavelengths, ofappropriately tuned photoreceptors, implanted in the eye; i. wherein atleast one of said plurality of wavelengths is used to transmit lightpower to at least one of said plurality of photoreceptors; j. wherein atleast one of said plurality of wavelengths is used to transmitinformation to at least one of said plurality of photoreceptors.
 18. Thelight amplifier of claim 17 wherein the image receiver and the firstconverter of said image into electrical signals is a video camera. 19.The light amplifier of claim 17 wherein said amplifier logarithmicallyamplifies said electrical signal.
 20. The light amplifier of claim 17wherein the transformer of the image size is a magnifier of the imagesize.
 21. The light amplifier of claim 20 wherein the magnifier of theimage size is an electronic magnifier.
 22. The light amplifier of claim20 wherein the magnifier of the image size is an optical zoom lens. 23.A light amplifier for use with photoreceptor-based implanted retinalprosthetics comprising: a. an image receiver; b. a first converter ofsaid image into electrical signals; c. an amplifier of said electricalsignals; d. an overall amplification of said electrical signal accordingto a definite functional relationship between input signal to theamplifier and an output signal from the amplifier; e. a transformer ofthe image size; f. a second converter of said amplified electricalsignal into a photon-based display; wherein said photons of said displayenter an eye through a pupil of said eye.
 24. The light amplifier ofclaim 23 wherein the image receiver and the first converter of saidimage into electrical signals is a video camera.
 25. The light amplifierof claim 23 wherein said amplifier logarithmically amplifies saidelectrical signal.
 26. The light amplifier of claim 23 wherein thetransformer of the image size is a magnifier of the image size.
 27. Thelight amplifier of claim 26 wherein the magnifier of the image size isan electronic magnifier.
 28. The light amplifier of claim 26 wherein themagnifier of the image size is an optical zoom lens.
 29. The lightamplifier of claim 2 or of claim 8 or of claim 17 or of claim 23 whereina first color of light to which the photoreceptors are particularlysensitive is amplified more than other color components; wherein thetransmission into the eye of said first color more efficientlystimulates said photoreceptors than a color other than the first color.30. The light amplifier of claim 2 or of claim 8 or of claim 17 or ofclaim 23 wherein only a black-and-white contrast image is displayed;wherein the white part of that image is logarithmically translated tothe color, i.e., wavelength, to which the photoreceptors are mostsensitive.
 31. The light amplifier of claim 2 or of claim 8 or of claim17 or of claim 23 wherein said wavelength is shifted toward or to thenear infrared or toward or to the near ultraviolet, according to whatoptimizes the response of the implanted photosensitive elements.
 32. Thelight amplifier of claim 2 or of claim 8 or of claim 17 or of claim 23wherein the second converter display emits directed photons which arescanned into the eye according to a pre-determined scan pattern, ontoultimately photoreceptor-activated electrodes, which stimulate retinalcells wherein knowledge of the color of the light originating from anexternal scene is used to-stimulate one or more living retinal cellswhich produces an appearance of that corresponding color.
 33. A methodfor enhancing the performance of a retinal prosthesis implanted in apatient's eye, comprising the steps of: implanting an array ofphotodetectors and a plurality of electrodes for stimulating retinalnerves; mounting a light amplifier external to the eye; responding to aninput image; producing an output image related to said input image by atransfer function G; positioning said light amplifier so that saidoutput image is incident on said implanted photodetector array; havingsaid plurality of electrodes respond to said output image incident onsaid photodetector array producing a sequence of negative and positiveelectrical pulses for application to said retinal nerves; generatingsuccessive pulses spaced in time by an interval Δt.
 34. A method formaking a light amplifier with photoreceptor-based implanted retinalprosthetics comprising the steps of: a. acquiring an image by camerameans; b. converting of said image into electrical signals; c.amplifying said electrical signal according to a functional relationshipbetween input signal and output signal; d. transforming the image sizeby transforming means; e. converting the amplified electrical signalinto a photon-based display; f. said photons of said display enter aneye through a pupil of said eye; g. implanting a plurality ofphotoreceptor with associated electronic elements and associatedelectrodes; h. receiving a single light wavelength by said plurality ofphotoreceptors and thereby activating said photoreceptors; l. activatinga plurality of electrodes with associated electronics by said pluralityof activated photoreceptors; j. producing a negative pulse followed by atime delay followed by a positive pulse by said electronics; k.introducing, thereby, a net charge of zero into the eye by the producedelectrical pulses.
 35. The method of claim 34 further comprising thesteps of a. receiving said image with a video camera and; b. convertingsaid image into electrical signals with said video camera.
 36. Themethod of claim 34 further comprising the step of transforming the imagesize by magnification.
 37. The method of claim 34 further comprising thestep of amplifying said electrical signal according to a logarithmicrelationship between input signal and output signal.
 38. The method ofclaim 34 further comprising the step of transforming the image size bymagnifying said image size.
 39. The method of claim 38 furthercomprising the step of electronically magnifying the image size.
 40. Themethod of claim 38 further comprising the step of optically magnifyingthe image size.
 41. The method of claim 38 further comprising the stepof optically magnifying the image size utilizing an optical zoom lens.42. A method for making a light amplifier with photoreceptor-basedimplanted retinal prosthetics comprising the steps of: a. acquiring animage by camera means; b. converting of said image into electricalsignals; c. amplifying said electrical signal according to a functionalrelationship between input signal and output signal; d. transforming theimage size by transforming means; e. converting the amplified electricalsignal into a photon-based display; f. interrupting the photon stream,periodically, from said photon-based display for periodic set amounts oftime; g. stimulating appropriately tuned light receivers implanted inthe eye, by means of a plurality of external-to-the-eye wavelengths oflight; h. shining on an equal number of types, as the number of theplurality of wavelengths, of said tuned light receivers; i. producing anequal amount of negative charge by one wavelength sensitive set ofphotoreceptors followed by a quiescent time produced by the cutting offof light by said shutter; producing an equal amount of positive chargeby another wavelength sensitive set of photoreceptors followed by aquiescent time produced by the cutting off of light by said shutter;whereby no net charge is introduced into the eye by this method; j.dividing up the net produced charge so the net charge adds up to zerofor the case of more than two wavelength sensitive photoreceptors. 43.The method of claim 42 further comprising the steps of a. receiving saidimage with a video camera and; b. converting said image into electricalsignals with said video camera.
 44. The method of claim 42 furthercomprising the step of transforming the image size by magnification. 45.The method of claim 42 further comprising the step of amplifying saidelectrical signal according to a logarithmic relationship between inputsignal and output signal.
 46. The method of claim 42 further comprisingthe step of transforming the image size by magnifying said image size.47. The method of claim 46 further comprising the step of electronicallymagnifying the image size.
 48. The method of claim 46 further comprisingthe step of optically magnifying the image size.
 49. The method of claim48 further comprising the step of optically magnifying the image sizeutilizing an optical zoom lens.
 50. The method of claim 42 furthercomprising the step of interrupting the photon stream periodically witha-mechanical shutter.
 51. The method of claim 42 further comprising thestep of interrupting the photon stream periodically with an electronicshutter.
 52. The method of claim 42 further comprising the step ofinterrupting the photon stream periodically with an electro-opticshutter.
 53. A method for making a light amplifier withphotoreceptor-based implanted retinal prosthetics comprising the stepsof: a. acquiring an image by camera means; b. converting of said imageinto electrical signals; c. amplifying said electrical signal accordingto a functional relationship between input signal and output signal; d.transforming the image size by transforming means; e. converting theamplified, electrical signal into a photon-based display; f.interrupting the photon stream, periodically, from said photon-baseddisplay for periodic set amounts of time; g. wherein a plurality ofexternal-to-the-eye wavelengths provides light stimulation to an equalnumber of types, as the number of the plurality of wavelengths, ofappropriately tuned photoreceptors, implanted in the eye; h. wherein atleast one of said plurality of wavelengths is used to transmit lightpower to at least one of said plurality of photoreceptors; i. wherein atleast one of said plurality of wavelengths is used to transmitinformation to at least one of said plurality of photoreceptors.
 54. Themethod of claim 53 further comprising the steps of a. receiving saidimage with a video camera and; b. converting said image into electricalsignals with said video camera.
 55. The method of claim 53 furthercomprising the step of amplifying said electrical signal according to alogarithmic relationship between input signal and output signal.
 56. Themethod of claim 53 further comprising the step of transforming the imagesize by magnifying said image size.
 57. The method of claim 56 furthercomprising the step of electronically magnifying the image size.
 58. Themethod of claim 56 further comprising the step of optically magnifyingthe image size.
 59. The method of claim 58 further comprising the stepof optically magnifying the image size utilizing an optical zoom lens.60. A method for making a light amplifier for use withphotoreceptor-based implanted retinal prosthetics comprising the stepsof: a. acquiring an image by camera means; b. converting of said imageinto electrical signals; c. amplifying said electrical signal accordingto a functional relationship between input signal and output signal; d.transforming the image size by transforming means; e. converting theamplified electrical signal into a photon-based display; f. said photonsof said display enter an eye through a pupil of said eye;
 61. The methodof claim 60 further comprising the steps of a. receiving said image witha video camera and; b. converting said image into electrical signalswith said video camera.
 62. The method of claim 60 further comprisingthe step of amplifying said electrical signal according to a logarithmicrelationship between input signal and output signal.
 63. The method ofclaim 60 further comprising the step of transforming the image size bymagnifying said image size.
 64. The method of claim 63 furthercomprising the step of electronically magnifying the image size.
 65. Themethod of claim 63 further comprising the step of optically magnifyingthe image size.
 66. The method of claim 64 further comprising the stepof optically magnifying the image size utilizing an optical zoom lens.67. The method of claim 34 or of claim 42 or of claim 53 or of claim 60further comprising the steps of amplifying a first color of light towhich a plurality of photoreceptors implanted in an eye is particularlysensitive, more so than other color components; transmitting said firstcolor into the eye; stimulating more efficiently said photoreceptorsthan would a color other than the first color.
 68. The method of claim34 or of claim 42 or of claim 53 or of claim 60 further comprising thesteps of displaying only a black-and-white contrast image; translatinglogarithmically the white part of that image to the color, i.e.,wavelength, to which the photoreceptors are most sensitive.
 69. Themethod of claim 34 or of claim 42 or of claim 53 or of claim 60 furthercomprising the steps of shifting a first wavelength toward or to thenear infrared or toward or to the near ultraviolet; optimizing, thereby,the response of the implanted photosensitive elements.
 70. The method ofclaim 34 or of claim 42 or of claim 53 or of claim 60 further comprisingthe steps of emitting directed photons from said photon based display;scanning said photons into the eye according to a pre-determined scanpattern; activating ultimately photoreceptor-activated electrodes bysaid photons; utilizing knowledge of the color of the light originatingfrom an external scene to determine said retinal cells to be stimulated;stimulating one or more living retinal cells which give an appearance ofthat corresponding color.
 71. A retinal prosthetic scanning laseralignment apparatus comprising a scanning laser; an imager oriented toreceive an image from the eye; wherein said imager receives an image ofthe scanning laser beam reflected from a retinal implant; said receiverimage electrically connected to a data processing unit; said dataprocessor unit processes information of said image; wherein said dataprocessor provides. real-time feedback information to a scanning lasercontrol unit.
 72. A retinal prosthetic scanning laser alignmentapparatus comprising fiduciary marks selected from a group consisting ofvariably spaced points and variably spaced lines; a scanning laser; adata processing unit; a scanning laser control unit; a reflected lightdetector which detects light and produces a corresponding electricalsignal; wherein scanning over the fiduciary marks by the scanning laserresults in a reflected beam of varying brightness; wherein saidreflected light detector detects said beam of varying brightness; saidreflected light detector is electrically connected to said dataprocessing unit; wherein said data processing unit controls the scanninglaser control unit to scan the laser correctly.
 73. A method for retinalprosthetic scanning laser alignment comprising the steps of: scanning ascanning laser over a retinal implant; imaging reflected beam from theretinal implant with an imager; processing information of said image bya data processing unit; providing real-time feedback information fromthe data processor unit to a scanning laser control unit; correcting themovement of the scanning laser by the scanning laser control unit.
 74. Amethod for retinal prosthetic scanning laser alignment apparatuscomprising the steps of: placing fiduciary marks selected from a groupconsisting of variably spaced points and variably spaced lines on theretinal implant; scanning a scanning laser over the retinal implant;detecting the reflected light with a reflected light detector; whereinscanning over the fiduciary marks by the scanning laser results in areflected beam of varying brightness; wherein said reflected lightdetector detects said beam of varying brightness; producing acorresponding electrical signal from the reflected light detector;sending the electrical signal to a data processing unit; processing theelectrical signal by the data processing unit; extracting theappropriate feedback correction information by processing the electricalsignal; sending the feedback correction information to the scanninglaser control unit; controlling the scanning laser control unit with thecorrection feedback information to scan the laser correctly across theretinal implant.